1. Field of the Invention
The present invention is in the field of drafting templates and guides. More particularly, this invention presents method and means to enable a draftsman to draw a series of concentric or similarly related closed circular figures without damage to the drafting medium.
2. Description of the Prior Art
Generally speaking, anyone using a pencil compass can draw any number of circles. However, professional drawing-board experience is essential in using a circle guide for drawing concentric circles of increasing or decreasing size for inking in drawings. In drawing such families of circles, it is difficult even for the experienced professional draftsman to obtain, e.g., 0.8-millimeter (mm) accuracy in spacing between circles, especially when inking-in is required.
Currently, when a professional draftsman is confronted with the problem of drawing a series of concentric circles, he has his choice of using a compass or a template of the existing art. Either choice has drawbacks. Drawing multiple circles with a compass tends to damage the paper where the point of the compass pierces the paper on repeated occasion as the different circles are drawn. To avoid this problem, the experienced draftsman may put a small piece of plastic on the drawing medium, and ground the point of the compass thereon. However, this method entails either the risk of the plastic slipping and destroying concentricity, or the uneconomical expenditure of time in affixing the plastic to the medium, such as by gluing or taping. Further, the repeated placement of the point of the compass does not always engage exactly the same position, leading to inaccuracies and lack of concentricity. While such inaccuracies may not be critical in conceptual drawings, they can introduce undesirable deviations from actual measurements in working shop drawings.
In using a template, each succeeding circle or other curvilinear figure must be centered by means of coordinating lines adjacent the appropriate hole in the template; however, no matter how careful the draftsman is, he is never completely sure that each succeeding figure is precisely centered or otherwise aligned. Further, the range of sizes available with current templates is somewhat restricted. In some cases, the lack of precision drawings can be critical, especially, as noted, where those drawings are used for shop and field work or in the presentation of patent illustrations. When the distance between adjacent figures approaches the thickness of the inked line, maintaining concentricity with existing templates also become marginal.
Another problem encountered with the apparatus and methods of the prior art is that a required series of circles to be drawn must be carefully planned. Generally, the smallest circle is drawn first, followed by those of increasing size. An attempt to proceed in the opposite fashion is difficult because the template, even though substantially transparent, often at least partly obscures the larger circle in the attempt to center the smaller. In the event that the draftsman discovers that he has to draw a series of circles concentric with one already drawn because of a change in specifications or for other reasons, it is not uncommon to have to remove the earlier-drawn figures and begin over. In the case where the circle has already been inked, the job becomes very difficult, and potentially damaging to the drafting medium.
Irrespective of the planning required in drawing circles with existing templates, a further problem arises where the range of the sizes of circles to be drawn is fairly great. Current practice requires the use of several templates, with the problems of careful alignment as already noted; further to that, however, is the circumstance that different templates may have different kinds of reference marks, which then requires that the draftsman pay particular attention to how he is aligning the template in order to avoid imprecision in the drawing.
While none of the problems discussed here are insurmountable, they are time-consuming, and detract from the productivity of the draftsman.
Even if the foregoing problems can be avoided, the draftsman now faces the problem of inking the pencil drawing without smearing the lines. Using templates of the prior art, the draftsman has to be careful not to permit the pen to contact the line where the template rests on the paper, or the ink will spread into that line by capillary action, causing his line to be thicker than he wants even assuming that he is able to control its actual placement with the necessary precision in the first place.
In present practice, when a draftsman makes an inked circle with a template, he places some kind of shim under the template to prevent its direct contact with the drawing medium to avoid capillarity. The use of the shim, however, invites both inaccuracy in the dimension of the circle and slippage of the template on the shim. To avoid the latter problem, the draftsman can tape the two together, but then tends to lose whatever time advantage he has gained by the use of the template.
Furuoka, in U.S. Pat. No. 3,568,327, shows what is essentially an amusement device for the production of epicyclic, hypocyclic and similar figures generated by the interrelation of a fixed reference point with another, moving point. By its very nature, the Furuoka device is incapable of producing concentric circles except by moving the template, a problem discussed hereinabove. The Furuoka apparatus further has means whereby the position of the template is fixed at specified angular intervals.
A device similar to that of Furuoka is described by Siegel in U.S. Pat. No. 3,699,660, differing from Furuoka in that it is adjustable to permit infinite variation among the designs generated. The Siegel device, however, is also limited in that it requires movement of the entire device to permit drawing of curvilinear figures related in size, but with a commonality of center or focus.
Jordan, in U.S. Pat. No. D 165,849, shows a drafting template whereby lines can be drawn at variable angles to an initial reference point or line. Use of the Jordan template requires the removal and replacement of screws to permit the template to be changed or the angle of a particular line altered.
None of the references discussed herein makes any provision for inking of a precision drawing, nor do they provide for the construction of a plurality of curvilinear figures without regard to the order in which the figures are drawn.